The propane industry has long been plagued with the knowledge that a residential propane distribution system could inadvertently release the combustible gas into the customer's house. If fortunate, this releasing event occurred when no one was home, and the fire or explosion which results from this gas release then only destroys the structure and personal possessions of the family. If unfortunate, the explosion is triggered by or associated with the re-entry of the individual into the gas-filled house, and the simple act of switching on a light results in horror, pain, and possibly death to the returning individuals. The propane industry offers relatively cost-efficient fuel to many homeowners who prefer to live in rural surroundings which are not supplied by a community gas distribution system. Accordingly, refillable propane tanks supplied by delivery trucks ideally meet the needs of many people throughout the world. Terrifying accounts of home explosions due to propane gas, however, have had a significant affect on the industry. Individuals sometimes select more costly and less convenient means of heating their homes or supplying energy to home appliances because of the risks associated with propane, as discussed further below.
There are numerous reasons why the need for improved safety systems to distribute propane or other combustible gases has not previously been satisfied. Partially because individuals do not always follow safety instructions or think about the consequences of their actions, many have felt that these risks could never be significantly reduced. Various actions and circumstances, only some of which are described below, can cause the inadvertent release of propane gas into a home. In one instance, the homeowner's backyard gas storage tank has run low on fuel, so that the pilot lights for the furnace and gas consuming appliances are extinguished. If the propane tank is then refilled while the owner is at work or otherwise absent from the home, the newly supplied gas is released un-burned into the house. The homeowner may subsequently return to his house and turn on a light, which causes a spark and explosion.
In another situation, a duplex tenant may vacate his side of the building with his propane tank empty, so that his appliance shutoff valve for supplying propane to the clothes dryer is left open, although no gas is escaping. The landlord or new tenant decides to refill the propane tank, which results in an open gas line into the building. The gas escapes into the adjoining duplex, injuring parties having no involvement in the explosion.
In other cases, the gas regulator is positioned adjacent the propane tank, and a line extends a substantial distance from the tank to the house, business, or other dwelling. Water in the line freezes, thereby cutting off the supply to the gas appliances. Later that day the ice blockage in the line thaws due to warming outdoor temperatures, and gas thereafter flows to the appliances with extinguished pilots, resulting in the same safety hazard.
In still another instance, the gas regulator to a house fails to serve its intended purpose of reducing gas pressure to the residential furnace and appliances, possibly because its vent port has become plugged with ice, wasps nests, or other debris. If the gas regulator fails, the high pressure flow of gas to the appliance typically extinguishes the pilot, and the high pressure gas is released to quickly fill a home, and may cause either an explosion or asphyxiation of sleeping individuals. Alternatively, the gas appliance may have an operable shut-off valve responsive to a burning pilot in order to maintain the supply of gas to the appliance, and this valve desirably thus closes when the pilot blows out. The fittings in the line between the regulator and the appliance are not capable of sealing against this higher pressure, however, so that gas leaking from these fittings nevertheless releases hazardous gas into the dwelling.
Fisher has marketed various safety shut-off devices, Types 5256-5259. Rockwell has marketed regulators with a low pressure cut-off, and shut-off valves designed for overpressure protection, for underpressure protection, or for both underpressure and overpressure protection. These devices have not, however, alleviated the problems discussed above, and improved systems, equipment, and techniques are required to lessen the risk of combustible gas usage throughout the world.
The present invention thus fills a need which has long existed. While the techniques of this invention unfortunately will not prevent all accidents involving the distribution or use of propane and other combustible gases, it will significantly reduce many of those risks which are today causing tremendous losses to both life and property.